1. Field of the Invention
This invention relates to small-sized vessels made of sheet metal which are suitable for the storage and carriage of pressurized liquid, pressurized gas and the like, and also relates to the manufacturing method of these vessels. More particularly, this invention is intended to provide small-sized pressure vessels of light weight and high tenacity at low manufacturing cost, without exerting severe stresses upon the sheet metal of which the vessels are made in the manufacturing process, and which vessels may be manufactured without subjecting the vessels to complicated machining processes.
2. Prior Art
In general, conventional type small-sized pressure vessels of less than 500 ml in capacity and 3 to 4 kg/cm.sup.2 in pressure resistivity are made of sheet metal to store and carry pressurized liquids such as carbonated drinking water and the like and also pressurized gases, such as low-pressure oxygen and the like. These vessels are chiefly rectangular in their longitudinal sections and are composed of two component portions made of a cap portion and a shell portion or composed of three component pieces of one cap portion and two shell portions. In order to make the conventional pressure vessel of two pieces, these two pieces are jointed together by means of a double-seaming process. Also, for the conventional three-piece type pressure vessels, the two shell pieces are united together at their seams by means of adhesives or soldering, and thereafter, the double-seaming process is used to circumferentially joint the united shell pieces and the cap piece together with sealing material. Moreover, when a pressure vessel of greater capacity of approximately 500 ml to 10 l is made, the sheet metal of which the pressure vessel is made is required to be increased in thickness according to the increase in the capacity of the pressure vessel. Thus, the pressure vessel is shaped so as to have an oval longitudinal section which is favorable from the viewpoint of the designing of the proper thickness of the material sheet metal used to shape the vessel. However, such a larger-sized pressure vessel does not differ from the foregoing small-sized pressure vessels in respect to jointing the shell pieces to the cap piece at their shoulder portions by the use of a double-seaming process.
The double-seaming process requires a metal plate of high rigidity at the seaming portion. Therefore, the thickness of a metal plate of which such a pressure vessel is made is required to be much greater in the seaming portion than that which is determined on the basis of the internal pressure of the vessel. For example, when a commercially available pressure vessel made of an aluminum alloy for beer has a thickness of approximately 0.55 mm in its bottom plate, it is required to have a thickness of approximately 0.7 mm in its upper shell plate. For this reason, the double-seaming construction of a pressure vessel requires an excessive amount of material, thereby increasing the manufacturing cost and the weight of an obtained pressure vessel. At the same time, the double-seaming construction has the decided disadvantage of reducing the cooling efficiency of, for example, a beverage within the pressure vessel. Furthermore, vessels produced by the double-seaming construction method have various serious disadvantages in that the pressure resistivity is limited to approximately 4 kg/cm.sup.2 as stated in the foregoing description, the sealing property is unstable, and a great number of machining steps are required to produce the vessel.